Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B9/00—Safety arrangements
  • G05B9/02—Safety arrangements electric
  • G05B9/03—Safety arrangements electric with multiple-channel loop, i.e. redundant control systems
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B11/00—Automatic controllers
  • G05B11/01—Automatic controllers electric
  • G05B11/36—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential
  • G05B11/42—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential for obtaining a characteristic which is both proportional and time-dependent, e.g. P.I., P.I.D.
• • G—PHYSICS
  • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
  • G16Z—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS, NOT OTHERWISE PROVIDED FOR
  • G16Z99/00—Subject matter not provided for in other main groups of this subclass

Definitions

• the present invention relates generally to continuous process control (CPC) and, more particularly, to dynamically configuring a CPC algorithm.
• PID proportional, integral, and derivative
• PID algorithms In industrial control systems there are many different types of PID algorithms. The most common types of PID algorithms are either "non-interacting" or "interacting". With an interacting algorithm, the proportional, integral, and derivative terms are combined in a way in which the terms interact, e.g., the terms are determined in series. With a non-interacting algorithm, the proportional, integral and derivative terms are combined in a way in which the terms do not interact, e.g., the terms are determined in parallel.
• Each algorithm type has benefits in different applications and in different control modes.
• different control objectives and operating conditions may arise that would make it desirable to switch from one control algorithm type to the other control algorithm type.
• An example would be a split- range temperature control where the PID output is split into two ranges; one for heating and one for cooling.
• the desired algorithm type for the heating range may be different from the desired algorithm type for the cooling range.
• CPC continuous process control
• a method for switching from a first control algorithm to a second control algorithm in a continuous process control system includes executing the first control algorithm, determining to switch from the first control algorithm to the second control algorithm, and executing the second control algorithm. For at least a first execution of the second control algorithm, at least one state variable used in the second control algorithm is adjusted.
• a process control system for controlling a process.
• the system includes a plurality of sensors configured to detect parameters of the process to be controlled, a plurality of local controllers configured to adjust the parameters of the process, and at least one central controller coupled to the sensors and to the local controllers.
• the central controller is configured to execute continuous process control algorithms to determine adjustments to be made by the local controller based on data from the sensors.
• the central controller is further configured to switch from a first control algorithm to a second control algorithm and, for at least a first execution of the second control algorithm, adjusting at least one state variable used in the second control algorithm.
• a controller for a continuous process control system includes a processor coupled to a memory.
• the processor is programmed to execute continuous process control algorithms to generate a PID output.
• the controller is further programmed to switch from a first control algorithm to a second control algorithm and, for at least a first execution of the second control algorithm, adjust at least one state variable used in the second control algorithm.
• Figure 1 is a schematic block diagram of a continuous process control system
• Figure 2 is a block diagram of a series-type PID algorithm
• Figure 3 is a block diagram of a parallel-type PID algorithm
• Figure 4 is a block diagram of series and parallel types of PID algorithms and a dynamic "bumpless" switch
• Figure 5 is a block diagram of a series-type PID algorithm for use with the dynamic bumpless switch illustrated in Figure 4.
• Figure 6 is a block diagram of a parallel-type PID algorithm for use with the dynamic bumpless switch illustrated in Figure 4.
• processor refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit, processor, or controller capable of executing the functions described herein.
• RISC reduced instruction set circuits
• ASIC application specific integrated circuits
• logic circuits and any other circuit, processor, or controller capable of executing the functions described herein.
• software and firmware are interchangeable, and include any computer program stored in memory for execution by a processor, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and nonvolatile RAM (NVRAM) memory.
• RAM memory random access memory
• ROM memory read only memory
• EPROM memory electrically erasable programmable read-only memory
• EEPROM memory electrically erasable programmable read-only memory
• NVRAM nonvolatile RAM
• FIG. 1 is a schematic block diagram of a continuous process control system 10.
• System 10 includes central controllers 12, or processors, coupled to an input/output (I/O) bus 14 and a fieldbus 16.
• I/O input/output
• fieldbus 16 The type of input/output bus 14 and fieldbus 16 selected depends on the particular type of system being controlled, and any one of numerous known and commercially available input/output buses and fieldbuses can be used.
• Input/output bus 14 and fieldbus 16 are coupled to various sensors 18 and local controllers 20 coupled to the system 10 to be controlled (not shown). Again, the particular sensors 18 and local controllers 20 depends on the particular type of system being controlled, as is well known in the art.
• Central controllers 12 also are coupled to an Ethernet based network 22.
• Engineering workstations 24 for use in connection with designing, creating, and maintaining system configuration are coupled to network 22.
• Operator consoles 26 for operators to monitor and control the process also are coupled to network 22.
• Database sub-system 28 also provides version control for process control strategies, including audit trail capabilities.
• FIG. 1 illustrates one of numerous example architectures for a continuous process control system.
• the present PID algorithms are not limited to use in connection with any one particular control system.
• An example of a known and commercially available control system is the Proficy® Process System commercially available from General Electric Company, Fairfield, Connecticut.
• central controllers 12 receive data from various sensors 18 located at selected data points of the system to be controlled. The received data is stored by database management sub-system 28. In addition, such received data can be used by central controllers 12 and local controllers 20 to make adjustments to components of the controlled system.
• Various control algorithms are stored in and executed by central controllers 12.
• continuous process control algorithms are stored in controllers and are executed by controllers in connection with providing continuous control of the system being controlled.
• the parameters referenced in the algorithms illustrated in Figures 2 and 3 are set forth below.
• PV(s) is the process variable to be controlled
• SP(s) is the setpoint, i.e., a desired value of the process variable
• K D is the derivative time in minutes
• N is the derivative filter parameter
• Kp is the proportional gain
• PD(s) is the proportional and derivative term
• Ki is the integral reset in repeats per minute
• PID(s) is the proportional and integral and derivative term
• the process variable to be controlled PV(s) and the setpoint for that process variable SP(s) are summed to obtain the difference ⁇ between the value of the variable and the setpoint.
• the derivative term D(s) is then generated and the proportional and derivative term PD(s) is then generated.
• the proportional and derivative term PD(s) is then summed with the integral term I(s) to generate the proportional and integral and derivative term PID.
• the proportional, integral and derivative terms are generated in series and are not independent of each other, i.e., the terms interact.
• Figure 3 illustrates a parallel PID algorithm.
• the process variable to be controlled PV(s) and the setpoint for that process variable SP(s) are summed to obtain the difference ⁇ between the value of the variable and the setpoint.
• the proportional term P(s), the integral term I(s), and the derivative term D(s) are then generated, independent of each other.
• the terms P(s), I(s), and D(s) are then summed to generate the proportional, integral and derivative (PID) term.
• the proportional, integral and derivative terms are generated in parallel and are independent of each other, i.e., the terms do not interact.
• FIG. 4 illustrates, in block diagram form, series 80 and parallel 90 types of PID algorithms and a dynamic "bumpless" switch 100.
• “bumpless” means to facilitate the avoidance of abrupt changes to the control system outputs that cause the controlled process to become unstable or end product degradation.
• one of the PID algorithms is selected by controller for execution, and controller causes switch to select the output from such selected algorithm to generate output PID.
• controller may determine to switch from the one PID algorithm to the other PID algorithm. Such determination can be made, for example, based on empirical data related to the process being controlled. When such determination is made, controller causes switch to select the output from the other algorithm to generate output PID.
• A(s) SP(s) ⁇ — — if the derivative term is based on error
• the PD term for the parallel algorithm is:
• PD SERIES A(s)- K p - B(s)- K P (3) and:
• A(S) - K P - B(S) - K P C(s)- E(s) + SP(s)- K P - PV(s)- K P (5)
• a ⁇ s) —C ⁇ s) + SP ⁇ s) (6)
• H_SP(s) —H_SP(s) + SP(s) (10)
• H _SP(s) K P [H _SP(s)- SP(s)] Q 1 N
• H_SP(s) is the last C(s) calculated before the switch and in equation (11) H_SP(s) is the last A(s) calculated before the switch from series to parallel, hence equations (10) and (11) remain valid. If the derivative is based only on the process variable, then H_SP(s) is equal to the setpoint in both algorithm types and no adjustment is necessary.
• H _PV(s) —H _PV(s)+ PV(s) (12)
• H _ PV(S) K P [H _ PV (s) - PV ⁇ s)] (13)
• H_PV(s) is the last E(s) calculated before the switch and in equation (13) H_PV(s) is the last B(s) calculated before the switch from series 80 to parallel 90, hence equation 12 and 13 remain valid.
• bumpless switching is achieved when switching from parallel 90 to series 80 by dynamically adjusting the state variables H_SP(s) and H_PV(s) using equations (10) and (12) respectively on the first execution of the series algorithm 80 after the switch. That is, for the first determination of the value PID using the series algorithm 80 subsequent to the switch, state variables H_SP(s) and H_PV(s) are adjusted using equations (10) and (12).
• the state variables will immediately respond to changes in the process variable and setpoint as governed by the series algorithm.
• Bumpless switching is achieved when switching from series 80 to parallel 90 by dynamically adjusting the state variables H_SP(s) and H_PV(s) using of equations (11) and (13) respectively on the first execution of the parallel algorithm 90 after the switch. That is, for the first determination of PID using the parallel algorithm 90 subsequent to the switch, state variables H_SP(s) and H_PV(s) are adjusted using equations (11) and (13). Again, after the bumpless switch, the state variables will immediately respond to changes in the process variable and setpoint as governed by the parallel algorithm.
• the above-described embodiments may be implemented using computer programming and/or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect is switching between different types (series and parallel) of control algorithms.
• Any such resulting program, having computer-readable code may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the above described embodiments.
• the computer readable media may be, for example, but is not limited to, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM), and/or any transmitting/receiving medium such as the Internet or other communication network or link.
• the article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network.

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